"Who built it?"
"The Time Lords. This is all that survives of their homeworld."
The Genesis Ark was a prison ship created by the Time Lords which, like the Doctor's TARDIS, was bigger on the inside than on the outside. The Time Lords used the Ark as a prison for millions of Daleks.
The Genesis Ark was sucked into the Void.
Once touched by a time traveler, the Ark became primed, which activated the Genesis Ark Mobile. Now, the Ark could be opened.
Dalek Sec elevated with the Ark into the sky because it needed an area of 30 square miles. The side of the Ark opened and revealed a dalek inside. The Ark spun around and around releasing daleks into the sky.
Genesis Ark Mobile Edit
When primed, the Genesis Ark Mobile was activated. It was a blue eye, similar to that of the Daleks, and spoke the same Dalek voice. Like the Daleks, the Ark could now move, elevate, and was protected by a shield similar to that of a Dalek.